Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $81.30   5.482%   $85.7569   $85.76   $85.75   $85.80  
  Purchase #2 $50.67   9.783%   $55.627   $55.63   $55.65   $55.60  
  Purchase #3 $113.39   11.140%   $126.0216   $126.02   $126.00   $126.00  
  Purchase #4 $116.73   8.482%   $126.631   $126.63   $126.65   $126.60  
  Purchase #5 $14.92   12.502%   $16.7853   $16.79   $16.80   $16.80  
  Purchase #6 $152.48   11.656%   $170.2531   $170.25   $170.25   $170.30  
  Purchase #7 $65.89   6.166%   $69.9528   $69.95   $69.95   $70.00  
  7 purchase totals = $595.38       $651.0277   $651.03   $651.05   $651.10